In the design of the airfoils of aircraft, it is desirable that the geometry of the airfoil profile and particularly the camber of the airfoil is adjustable or adaptable to the varying boundary conditions prevailing during the course of a flight. In one class of conventional airfoils, an adjustment of the position or configuration of the airfoil trailing edge is only carried out during take-off and landing phases.
German Patent 4,107,556 (Gartelmann et al.) discloses one possible arrangement of a moveable landing flap on an airfoil. In this known arrangement, the landing flap is rotatably connected to a carriage that is movably arranged on a guide rail, whereby the landing flap is slidably movable, while a pivotally connected lever varies the angle of the landing flap during its sliding extension movement. During the take-off or landing phase of the aircraft, the landing flap is extended toward the rear, whereby the airfoil surface area is enlarged and the profile contour and particularly the camber of the airfoil is altered due to the variation of the angle of the landing flap.
Moreover, it is also desirable to be able to modify the trailing edge of the airfoil during cruise flight in order to better utilize or achieve the optimum flow potential of the wings of commercial transport aircraft. For this reason, arrangements have also become known, which make it possible to vary the contour of the airfoil trailing edge during cruise flight. For example, German Patent Document 3,527,497 describes a trailing edge construction in which a flap is slidably arranged in a guide channel, with an outrigger pivotally connected to supporting structures of the airfoil wing, whereby a sliding extension of the flap in the guide channel achieves a variation of the trailing edge contour. However, this known arrangement provides for a variation of the trailing edge contour in only one direction, and it is not possible to achieve a freely selectable control or actuation of the trailing edge without limitations. Particularly, it is not possible to achieve a continuously curved, kink-free or bend-free profile geometry of the airfoil.
German Patent Publication 3,101,847 discloses that it is known to increase the lift of a lifting airfoil and/or to reduce the airflow disrupting mechanisms, by embodying the trailing edge as a flap that can be pivotally adjusted about internally arranged pivot axes extending in the span width direction, by means of internally arranged control arms extending in the airflow direction. However, it has been found that disadvantageous lever arms result from the internally arranged axes and control arms while carrying out the flap adjustment movements. For this reason, large actuation forces are necessary.
German Patent 703,375 (Weber) describes a trailing edge control surface arranged to be pivotable about a pivot axis that extends in the span width direction. The force and motion transmission to the control surface is carried out via a push rod and a lever that pivot a drive shaft arranged along the pivot axis, which in turn tilts a drive lever that carries a motion actuator member arranged within the control surface. The control surface is formed by a rearward extension of the cover skins of the airfoil with the space therebetween filled out with foam rubber, so that this trailing edge control surface is flexible or bendable about the pivot axis. The two cover skins are respectively slidably connected to the motion actuator member, so that tilting of the actuator member applies a force within the control surface to deflect the same. The control surface is especially a control surface connected to a horizontal stabilizer or a vertical stabilizer of an aircraft tailplane. If the control surface is connected to a lifting wing airfoil via the pivot axis, it is not possible to achieve a kink-free of bend-free deflection of the control surface, since the deflection takes place about the pivot axis, especially for large deflections whereby the cover skins may directly contact the drive lever, the actuator member or even the drive shaft.
U.S. Pat. No. 4,247,066 (Frost et al.) describes a bendable, variable camber airfoil comprising flexible cover skins slidably connected onto airfoil ribs embodied as trusslike bendable beams. Namely, each rib comprises a plurality of relatively movably interconnected truss members and a jackscrew drive mechanism operatively connected to the truss members. By actuating the jackscrew, the bendable beam forming each rib can be bent or deflected, while the flexible cover skins slidably and flexibly follow the contour of the deflected rib beam so as to achieve a variation in the airfoil camber and surface curvature. The known bending beam arrangement is quite complicated, expensive, and heavy relative to a conventional fixed rib construction. It is also questionable whether the arrangement of articulately connected truss members and a jackscrew mechanism provides sufficient rigidity and structural strength for meeting the applicable requirements.
It has been found that the several different known arrangements are unable to achieve a continuous, kink-free curving or bending of the airfoil profile and particularly the profile of the trailing edge portion. Moreover, in the arrangements in which the drive for varying the trailing edge contour is arranged within the airfoil itself, this leads to disadvantageous transmission ratios, e.g. lever ratios, and consequent high actuation forces. Furthermore, the internally arranged adjustment devices in most cases are characterized by a rather high weight, and are difficult to access for maintenance purposes. Any arrangement in which a movable trailing edge is actuated by means of a control arm or rod and lever linkages is rather complicated and costly, and comprises many parts that are subject to rapid wear.